Stunning the Appendage: Pre-Emptive Ablation May Cut Peridevice Leaks After LAAO
New nonrandomized data suggest that ablating the left atrial appendage before closure devices are deployed shrinks residual flow around the implant — and the physiologic story behind it is straightforward.
Peridevice leaks remain the most persistent nuisance in left atrial appendage occlusion (LAAO) therapy despite a decade of device refinement.
A nonrandomized study called STUN-AF, presented at New York Valves 2026, offers a plausible fix.
Among 317 patients undergoing combined atrial fibrillation ablation and appendage closure, ablating the appendage itself before implanting the occluder nearly doubled the rate of complete appendage sealing by four months.
By one year, 96% of appendage-ablated patients had no detectable leak on imaging, compared with 58% of those who skipped the extra step.
Why Peridevice Leaks Matter
Roughly a quarter to a third of patients have some residual flow around a closure device on follow-up imaging, even with modern iterations like Watchman FLX Pro.
That residual flow is not a benign imaging footnote.
Pooled five-year follow-up from the original Watchman device trials found that patients with any leak up to 5 mm at one year had roughly double the risk of ischemic stroke or systemic embolism compared with patients whose appendages were fully sealed, an effect driven mainly by nondisabling strokes.
A separate meta-analysis using a strict CT definition of patency found that more than half of patients had some detectable flow behind the device at a mean of roughly five months, and patency tracked with higher thromboembolism and mortality.
The takeaway echoed by the presenting electrophysiologist was blunt: leaks are bad, and the goal of the procedure should be true anatomic obliteration, not just a leak below an arbitrary size cutoff.
The STUN-AF Hypothesis
Beyond anatomic mismatch between device and appendage, investigators suspected that residual mechanical contraction of the appendage itself was working against device healing.
A contracting appendage can create intermittent flow around an otherwise well-seated device and interfere with the endothelialization needed to seal it permanently.
The STUN-AF concept was to electrically stun the appendage — eliminating its contractile motion — before deploying the occluder, so the device sits still long enough to heal in place.
Study Design and Findings
STUN-AF enrolled 317 patients (mean age 76 years, 58% men) with atrial fibrillation or flutter undergoing concomitant pulsed-field ablation (PFA) and LAAO at three US centers.
Pulmonary vein isolation was performed predominantly with the Farawave catheter (62% of cases) and the Sphere-9 catheter (34%), with LAAO performed using Watchman FLX or FLX Pro devices.
After standard pulmonary vein isolation, 70% of patients underwent additional ablation targeting the appendage itself before device implantation, while 30% proceeded directly to closure.
On multivariable analysis, prior appendage ablation was the only independent predictor of complete sealing at four months, cutting the odds of any leak by roughly 80%.
Mechanistically, appendage ablation measurably reduced LAA emptying velocities, and lower velocities independently tracked with lower odds of leak — supporting residual contractility as a modifiable target.
Adverse events were reassuringly low and similar between groups, with 98% of patients free of any periprocedural complication.
There was a numerically lower stroke rate at three months in the ablation group (0.5% vs 2.1%), though the study was explicitly underpowered to detect differences in hard clinical outcomes.
Table 1. STUN-AF at a Glance
| Parameter | Detail |
|---|---|
| Population | 317 patients with AF/flutter undergoing same-session PFA + LAAO |
| Mean age / sex | 76 years; 58% men |
| Intervention | Additional LAA-directed ablation before device implantation (70% of cohort) |
| Comparator | LAAO without prior LAA ablation (30% of cohort) |
| No-leak rate, 4 months | 71% (ablation) vs 36% (no ablation), P < 0.001 |
| No-leak rate, 12 months | 96% (ablation) vs 58% (no ablation), P < 0.001 |
| Periprocedural adverse events | 98% free of events overall; no between-group difference |
| Key limitation | Nonrandomized; underpowered for stroke/clinical endpoints |
Where This Fits in Practice
The presenting investigator noted that appendage ablation is now performed routinely at the enrolling center whenever a patient is already undergoing combined AF ablation and LAAO in the same session.
The economics are a different story for isolated LAAO procedures, where opening an additional ablation catheter purely to stun the appendage is not currently reimbursed and unlikely to be practical.
That reimbursement gap is not hypothetical: the 2026 Medicare Physician Fee Schedule proposed cutting the work relative value units for LAAO (CPT 33340) by roughly 27%, a change professional societies have publicly opposed as a stroke-prevention access issue.
On the hospital side, CMS has already created a dedicated concomitant MS-DRG (317) that bundles ablation and appendage closure performed together, which is the payment structure under which same-session LAA-ablation-before-LAAO would most naturally fit.
An outside discussant, an interventional cardiologist unaffiliated with the trial, agreed that a hypercontractile appendage is a familiar culprit when a device "does not sit right," and that stilling the appendage helps it anchor.
Both the presenter and discussant called for a randomized trial to confirm a clinical benefit, while acknowledging that low absolute stroke rates make such a trial logistically difficult.
The Device and Company Landscape
For physician-investors tracking the structural heart and electrophysiology space, this data point sits at the intersection of two fast-growing device categories inside the same procedure.
Boston Scientific supplies both the dominant LAAO platform and one of the two leading PFA catheters used in the study, giving it exposure on both sides of a combined procedure.
Medtronic's Affera mapping and ablation system with the Sphere-9 catheter was the second-most-used PFA platform in the cohort, and offers a dual pulsed-field/radiofrequency option in a single catheter.
Table 2. Devices and Companies Referenced in STUN-AF
| Device | Category | Manufacturer (Ticker) | Share Price | Analyst Consensus |
|---|---|---|---|---|
| Watchman FLX / FLX Pro | LAAO occluder | Boston Scientific (NYSE: BSX) | ~$45 | Buy; 12-mo target ~$75 |
| Farawave / FARAPULSE | Pulsed-field ablation catheter | Boston Scientific (NYSE: BSX) | ~$45 | Buy; 12-mo target ~$75 |
| Sphere-9 / Affera | Dual-energy (PFA + RF) mapping and ablation catheter | Medtronic (NYSE: MDT) | ~$79 | Buy; 12-mo target ~$98 |
Both companies' PFA franchises are still maturing commercially, and the LAAO growth trajectory itself has recently been a point of investor scrutiny, with several analysts trimming price targets after commentary on slowing Watchman utilization.
As always, published analyst consensus ratings and price targets are snapshots that shift with each earnings cycle, and past device adoption trends are not a guarantee of future procedural volumes or share performance.
A 76-year-old with paroxysmal atrial fibrillation and a prior gastrointestinal bleed on anticoagulation is scheduled for same-day pulmonary vein isolation and left atrial appendage closure.
Pre-procedural imaging shows a windsock-shaped appendage with brisk emptying velocities, a morphology previously associated with higher rates of residual device leak.
Based on the STUN-AF experience, the operator elects to extend ablation to the ostium and proximal appendage after pulmonary vein isolation and before device deployment.
Follow-up transesophageal echocardiography at four months shows complete appendage sealing, and the patient is transitioned off anticoagulation per protocol.
In a nonrandomized 317-patient series, ablating the left atrial appendage before device closure roughly doubled complete-sealing rates at four months and nearly closed the gap entirely by one year.
The physiologic rationale — that residual appendage contractility disrupts device healing — is biologically coherent and measurable via emptying velocities on imaging.
Clinical outcome data remain underpowered, reimbursement for isolated LAAO does not currently support routine adjunctive ablation, and a randomized trial is unlikely given low event rates, so this remains a reasonable adjunct in combined-procedure patients rather than a new standard of care.
References
- STUN-AF: Ablation Before LAAO May Reduce Peridevice Leaks. TCTMD, July 2026.
- Peridevice Leaks After LAA Occlusion Signal Poorer 5-Year Outcomes. TCTMD.
- New York Valves 2026 Late-Breaking Research Preview. Cardiovascular Research Foundation.
- WATCHMAN FLX Pro Left Atrial Appendage Closure Device. Boston Scientific.
- FARAWAVE Pulsed Field Ablation Catheter. Boston Scientific.
- Sphere-9 Catheter, Affera Mapping and Ablation System. Medtronic.
- CMS Finalizes New Concomitant MS-DRG for LAAO and Ablation for Atrial Fibrillation. Heart Rhythm Society.
- CMS Reduces LAAO Value in Proposed 2026 Medicare Physician Fee Schedule. American College of Cardiology.
- Boston Scientific Corporation (BSX) Stock Overview. StockAnalysis.com.
- Medtronic plc (MDT) Stock Overview. StockAnalysis.com.
Physician education disclaimer: This article summarizes publicly reported conference data and published literature for physician education. It is not a substitute for review of full trial methodology, primary sources, or institutional protocols, and should not be used to guide individual patient care decisions in isolation.
Financial education disclaimer: Company, ticker, and market data are provided for general financial education only and do not constitute investment advice or a recommendation to buy or sell any security. Share prices and analyst ratings are time-sensitive snapshots that change frequently; past performance does not predict future results. Readers should consult a licensed financial advisor before making investment decisions.
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